High Pressure Liquid Chromatography (i.e., "HPLC") has in the past been extensively developed and applied in the field of ion analysis. Technical literature relating to prior HPLC methods for ion analysis relevant to this invention is identified below:
__________________________________________________________________________ Reference Number Source Identification __________________________________________________________________________ (I) "ANALYTICAL ION-EXCHANGE PROCEDURES IN CHEMISTRY AND BIOLOGY, Theory, Equipment, Techniques" By Joseph X. khym, - 1974 Ed., Published by PRENTICE-HALL, INC. of Englewood Cliffs, New Jersey 07632; (II) N. E. Skelly, Anal. Chem., 54 (1982) 712; (III) I. Molnar, H. H. Nauer and D. Wilk, J. Chromatogr., 201 (1980) 225; (IV) H. J. Cortes, J. Chromatogr., 234 (1982)517; (V) H. Small, T. S. Stevens and W. C. Bauman, Anal. Chem., 47 (1975) 1801; (VI) H. Small and T. E. Miller, Anal. Chem., 54 (1982) 462; (VII) United States Letters Patent No. (i.e., "U.S."): 3,920,397; (VIII) T. S. Stevens, J. C Davis, and H. Small, Anal. Chem., 53 (1981) 1488; (IX) United States Letters Patent 4,383,047;; (X) United States Letters Patent 4,414,842; (XI) P. R. Haddad and A. L. Heckenberg, J. Chromatogr., 252 (1982) 177; (XII) "ION EXCHANGE" by F. Helfferich, 1962 Ed., Published by McGraw-Hill Book Company, Inc. of New York City (New York) 10017; and (XIII) "INTRODUCTION TO MODERN LIQUID CHROMATOGRAPHY" by L. Snyder and R. Kirkland, - 1979 Ed., Published by John Wiley & Sons, - New York City (New York) 10017. __________________________________________________________________________
As is brought forth in Ref. (II), HPLC analysis of inorganic and organic ions which absorb in the ultraviolet region has been accomplished on reverse phase liquid chromatographic columns having pendant functional ion-exchange groups. Ref. (IV) is illustrative of a similar analysis when relying on direct ultraviolet light (i.e., "UV") detection after separation on an amino column. Those anions and cations which do not absorb in the UV region can be determined by conductimetric detection, as is evidenced, e.g., by Refs. (V) and (VIII). Ion analysis is also possible by the use of the more recent liquid chromatographic procedure known as Indirect Photometric Chromatography (i.e., "IPC").
Small and Miller reported IPC in Ref. (VI) and in patent Ref. (X). As brought out in their original work, sensitive detection of the analyte ions is obtained using dilute eluents according to the expression: ##EQU1## wherein: C.sub.s is the concentration of the sample ion being analyzed;
N is the random noise which is generated or occurs in the system; and PA1 C.sub.e is the monitor/displacing ion concentration of the eluent ion. PA1 B=the inflection point, in terms of A, of the curve of k' of an ion of interest in an analysis versus A for a fixed eluent displacing ion concentration used for the analysis; PA1 C=the molar concentration of the eluent displacing ion used for the analysis.
However, the use of diluent eluents to obtain high sensitivity in IPC can lead to high k' values when used together with conventional strong base and strong acid ion-exchange chromatography columns. These strong base (and acid) ion-exchange columns can be modified, e.g., by physically shortening the column to reduce k', but this also produces a detrimental reduction in the theoretical plate count of the shortened column. The invention is concerned with overcoming this disadvantage of IPC procedures.